1. Field of the Invention
This invention relates generally to a system and method for determining faults and wear on an electric motor and, more particularly, to a system and method for determining faults and wear on an electric motor that includes monitoring the mean and variance of the motor current.
2. Discussion of the Related Art
DC motors provide the driving force for many consumer products. For example, DC motors are used in automobiles for controlling windows, windscreen wipers, electric power assisted steering, fuel pumps, etc. DC motors for these applications are subject to various faults and failure modes, both mechanical and electrical, and a gradual degradation of the motor, which leads to loss of motor performance. Typical faults include bearing failures, brush and commutator wear, loss of magnetic flux, winding short or open-circuit failure, magnet demagnetization, mechanical rotor eccentricities, such as bent rotor or damaged bearings, etc.
Several techniques have been developed in the art to identify these types of motor faults, such as using a frequency response, Fourier and wavelet transforms, etc. Motor current signature analysis (MCSA) is a widely used tool for condition monitoring of electrical machines. MCSA has been applied to the detection of a number of different faults in the bearings, stator and eccentricities of induction motors. This technique employs a frequency response method that can isolate the fault to the specific cause. Other known techniques provide a review of condition monitoring and fault diagnosis approaches for electrical machines.
It is desirable for vehicle motor applications to monitor the gradual degradation and failure of electric motors. However, the known techniques discussed above for accomplishing this require high sampling rates and complex signal processing, which typically are not available from a vehicle engine controller for this purpose. In many situations, it is only necessary to determine the fault of the DC motor and is not necessary to root cause the fault to the level of the specific fault. In other words, because a failed motor will typically be replaced, it is not necessary to know what the cause of the failure is, only that there is a failure. Therefore, it is desirable to provide a technique for monitoring the degradation of a vehicle electric motor during vehicle operation that does not require fast sampling rates.